1. Field of the Invention
This invention relates to an improved fluorescent gas-discharge color display panel and, more particularly, to an improved mixture of the discharge gas for use therein, and which produces discharges of a wavelength capable of producing a color display by exciting the fluorescent material within the panel.
2. Description of the Related Art
Various types of fluorescent gas-discharge color display panels utilizing an ultra violet light generated by the gas-discharge, either DC (direct current) driven or AC (alternating current) driven, have been developed and are in use for displaying characters as well as images. As is well known, a color display is achieved by providing plural kinds of fluorescent materials in the discharge panel, each of which is excited by the ultra violet light generated by a respectively associated gas discharge.
A typical configuration of a panel utilizing a surface discharge, such as shown in FIGS. 1 and 2 hereof and also as disclosed in U.S. Pat. No. 4,638,218 by the present inventor, offers promising potential as a successful gas-discharge color display panel utilizing plural fluorescent materials. Basically, in the surface discharge display panel and as shown in FIG. 1, the discharge electrodes 3, 4 and 7 are provided on the inner surface of only one, i.e., the single substrate 1, of the pair of two substrates 1 and 2 comprising the panel envelope, and a fluorescent material layer 8 is provided on the inner surface of the other, facing, substrate 2. The fluorescent material layer 8 is excited by the ultra violet light generated by the gas discharges produced between the electrodes on the facing substrate 2, the color of the emitted light being determined by the specific fluorescent material. The electrodes 3 and 4 and the electrodes 7 are arranged in mutually orthogonal X and Y directions on the substrate 1, and are isolated from each other and from the gas discharge space. Particularly, the surfaces of these electrodes are covered with an insulating material layer 10 having high secondary-electron emissivity, such as magnesium oxide (MgO). Since the discharges occur between the electrodes on the substrate 1, this configuration prevents the fluorescent material layer 8 from being directly bombarded by the ions produced by the discharges and contributes to a long operating life of the fluorescent material.
Discharge gases which emit an ultra violet light for exciting the fluorescent material which, in turn, emits a visible light, have been extensively studied, as disclosed by Kagami et al. in U.S. Pat. No. 4,085,350. A well-known gas composition, or mixture, comprising two components, namely helium and xenon (He and Xe), has been used for a multiple color display discharge panel in which the purity of the emitted color is deemed highly important. The xenon gas functions to lower the required levels of both the discharge firing voltage and the discharge sustain voltage, in accordance with the well-known Penning effect. In this gas composition, however, the heavy xenon ions bombard the surface of the MgO insulating layer which is coated over the electrodes. Accordingly, the MgO layer deteriorates quickly and thus the panel has a short operating life.
Consideration has been given to adding argon gas as a third constituent to the above two-component gas mixture; since heavier than helium, argon effectively would function to lower the energy of the xenon ions which bombard the MgO surface. However, the resultant three-component gas mixture including argon introduces the problem of increasing the operating voltages of the panel.
An alternative gas mixture of two components (Ne+0.2% Xe--the percentage, as therein expressed and as appears hereinafter, indicating the ratio of the partial pressure of the gas) also has been used, particularly for exciting a mono- or single-color display discharge panel. The presence of the neon gas, however, results in the gas discharges emitting an orange light which, since in the visible spectrum, deteriorates the purity of the color of the light emitted by the fluorescent material layer.
A practical gas-discharge panel, and particularly one employing a fluorescent material layer for producing a color display as is here pertinent, must have a long operating life, low operating voltages, a sufficient level of luminance, or brightness, and sufficient color purity. Presently existing devices, however, have not achieved the simultaneous satisfaction of all of these requirements and thus there is a continuing need for improved such gas-discharge color display panels.